Process to Recover Alcohol with Secondary Reactors for Esterification of Acid

ABSTRACT

A process for recovering ethanol obtained from the hydrogenation of acetic acid. The crude ethanol product is separated in a column to produce a distillate stream comprising acetaldehyde and ethyl acetate and a residue stream comprising ethanol, acetic acid, ethyl acetate and water. Unreacted acetic acid can be reduced or removed through configurations of esterification secondary reactors. The ethanol product is recovered from the residue stream.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. Nos.13/094,588, filed on Apr. 26, 2011; 13/094,488, filed on Apr. 26, 2011;and 13/292,914, filed on Nov. 9, 2011, the entire contents anddisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingalcohol and, in particular, to a process for recovering ethanol whilereducing or eliminating acid recovery and/or acetal separation steps.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from organic feedstocks, such as petroleum oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosicmaterials, such as corn or sugar cane. Conventional methods forproducing ethanol from organic feed stocks, as well as from cellulosicmaterials, include the acid-catalyzed hydration of ethylene, methanolhomologation, direct alcohol synthesis, and Fischer-Tropsch synthesis.Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosicmaterials, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol, whichis suitable for fuels or human consumption. In addition, fermentation ofstarchy or cellulosic materials competes with food sources and placesrestraints on the amount of ethanol that can be produced for industrialuse.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacids, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. Also, thehydrogenation can form acetals, such as diethyl acetal, as an unwantedbyproduct which can be fed back to the reactor system, increasing energyrequirements. In addition, when conversion is incomplete, acid remainsin the crude ethanol product, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol stream and a stream of acetic acid andethyl acetate, which is recycled to the hydrogenation reactor.

U.S. Pat. No. 7,842,844 describes a process for improving selectivityand catalyst activity and operating life for the conversion ofhydrocarbons to ethanol and optionally acetic acid in the presence of aparticulate catalyst, said conversion proceeding via a syngas generationintermediate step.

The need remains for improved processes for recovering ethanol from acrude product obtained by reducing alkanoic acids, such as acetic acid,and/or other carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In one embodiment of the present invention is directed toward a processfor producing ethanol comprising: hydrogenating acetic acid and/or anester thereof in a reactor in the presence of a catalyst to form a crudeethanol product comprising ethanol, water, ethyl acetate and aceticacid. A portion of the crude ethanol product is esterified in asecondary reactor to esterify unreacted acetic acid and form anesterified stream. The embodiment involves separating a portion of theesterified stream in a first distillation column to yield a firstdistillate comprising acetaldehyde and ethyl acetate, and a firstresidue comprising ethanol, acetic acid, ethyl acetate and water,followed by separating a portion of the first residue in a seconddistillation column to yield a second residue comprising acetic acid andan overhead vapor comprising ethanol, ethyl acetate and water. Nextwater is removed from at least a portion of the overhead vapor to yieldan ethanol mixture stream having a lower water content than the at leasta portion of the overhead vapor. The at least a portion of the ethanolmixture stream is separated in a third distillation column to yield athird distillate comprising ethyl acetate and a third residue comprisingethanol and less than 8 wt. % water, e.g., less than 3 wt. % water orless than 0.5 wt. % water.

Another embodiment of the present invention involves a process forproducing ethanol comprising: hydrogenating acetic acid and/or an esterthereof in a reactor in the presence of a catalyst to form a crudeethanol product comprising ethanol, water, ethyl acetate and aceticacid; separating a portion of the crude ethanol product in a firstdistillation column with a side car reactor for esterifying acetic acidin a sidedraw from the first distillation column, wherein the firstdistillation column yields a first distillate comprising acetaldehydeand ethyl acetate, and a first residue comprising ethanol, acetic acid,ethyl acetate and water; separating a portion of the first residue in asecond distillation column to yield a second residue comprising aceticacid and an overhead vapor comprising ethanol, ethyl acetate and water;removing water from at least a portion of the overhead vapor to yield anethanol mixture stream having a lower water content than the at least aportion of the overhead vapor; and separating at least a portion of theethanol mixture stream in a third distillation column to yield a thirddistillate comprising ethyl acetate and a third residue comprisingethanol and less than 8 wt. % water, e.g., less than 3 wt. % water orless than 0.5 wt. % water.

A further embodiment of the present invention involves a process forproducing ethanol comprising: hydrogenating acetic acid and/or an esterthereof in a reactor in the presence of a catalyst to form a crudeethanol product comprising ethanol, water, ethyl acetate and aceticacid; separating a portion of the crude ethanol product in a firstdistillation column with an integrated reboiler reactor for esterifyingacetic acid in a reboiler loop of the first distillate column, whereinthe first distillation column yields a first distillate comprisingacetaldehyde and ethyl acetate, and a first residue comprising ethanol,acetic acid, ethyl acetate and water; separating a portion of the firstresidue in a second distillation column to yield a second residuecomprising acetic acid and an overhead vapor comprising ethanol, ethylacetate and water; removing water from at least a portion of theoverhead vapor to yield an ethanol mixture stream having a lower watercontent than the at least a portion of the overhead vapor; andseparating at least a portion of the ethanol mixture stream in a thirddistillation column to yield a third distillate comprising ethyl acetateand a third residue comprising ethanol and less than 8 wt. % water,e.g., less than 3 wt. % water or less than 0.5 wt. % water.

An additional embodiment of the invention involves a process forproducing ethanol comprising: hydrogenating acetic acid and/or an esterthereof in a reactor in the presence of a catalyst to form a crudeethanol product comprising ethanol, water, ethyl acetate and aceticacid; separating a portion of the crude ethanol product in a firstdistillation column to yield a first distillate comprising acetaldehydeand ethyl acetate, and a first residue comprising ethanol, acetic acid,ethyl acetate and water; esterifying a portion of the first residue inan esterification reactor to esterify acetic acid and form an esterifiedfirst residue; separating a portion of the esterified first residue in asecond distillation column to yield a second residue comprising aceticacid and an overhead vapor comprising ethanol, ethyl acetate and water;removing water from at least a portion of the overhead vapor to yield anethanol mixture stream having a lower water content than the at least aportion of the overhead vapor; and separating at least a portion of theethanol mixture stream in a third distillation column to yield a thirddistillate comprising ethyl acetate and a third residue comprisingethanol and less than 8 wt. % water, e.g., less than 3 wt. % water orless than 0.5 wt. % water.

In another aspect of the present invention, there is provided a processfor producing ethanol comprising hydrogenating acetic acid and/or anester thereof in a reactor in the presence of a catalyst to form a crudeethanol product comprising ethanol, water, ethyl acetate and acetal,passing a portion of the crude ethanol product through a secondaryreactor to hydrolyze acetal and esterify acetic acid and produce a feedstream, separating a portion of the feed stream in a first distillationcolumn to yield a first distillate comprising acetaldehyde and ethylacetate, and a first residue comprising ethanol, acetic acid, ethylacetate and water, separating a portion of the first residue in a seconddistillation column to yield a second residue comprising acetic acid andan overhead vapor comprising ethanol, ethyl acetate and water, removingwater from at least a portion of the overhead vapor to yield an ethanolmixture stream having a lower water content than the at least a portionof the overhead vapor, and separating at least a portion of the ethanolmixture stream in a third distillation column to yield a thirddistillate comprising ethyl acetate and a third residue comprisingethanol and less than 8 wt. % water, e.g., less than 3 wt. % water orless than 0.5 wt. % water.

In yet another aspect of the present invention, there is provided aprocess for producing ethanol comprising hydrogenating acetic acidand/or an ester thereof in a reactor in the presence of a catalyst toform a crude ethanol product comprising ethanol, water, ethyl acetateand acetal, separating a portion of the crude ethanol product in a firstdistillation column with a side car reactor for hydrolyzing acetal andesterifying acetic acid in a sidedraw from the first distillationcolumn, wherein the first distillation column yields a first distillatecomprising acetaldehyde and ethyl acetate, and a first residuecomprising ethanol, acetic acid, ethyl acetate and water, and separatinga portion of the first residue in a second distillation column to yielda second residue comprising acetic acid and an overhead vapor comprisingethanol, ethyl acetate, and water. The process further comprisesremoving water from at least a portion of the overhead vapor to yield anethanol mixture stream having a lower water content than the at least aportion of the overhead vapor, and separating at least a portion of theethanol mixture stream in a third distillation column to yield a thirddistillate comprising ethyl acetate and a third residue comprisingethanol and less than 8 wt. % water, e.g., less than 3 wt. % water orless than 0.5 wt. % water.

In yet another aspect of the present invention, there is provided aprocess for producing ethanol comprising hydrogenating acetic acidand/or an ester thereof in a reactor in the presence of a catalyst toform a crude ethanol product comprising ethanol, water, ethyl acetateand acetal, hydrolyzing a portion of the crude ethanol product in ahydrolysis reactor to hydrolyze acetal and form a hydrolyzed stream, andseparating a portion of the hydrolyzed stream in a first distillationcolumn to yield a first distillate comprising acetaldehyde and ethylacetate, and a first residue comprising ethanol, acetic acid, ethylacetate and water. The process comprises esterifying a portion of thefirst residue in an esterification reactor to esterify acetic acid andform an esterified first residue separating a portion of the esterifiedfirst residue in a second distillation column to yield a second residuecomprising acetic acid and an overhead vapor comprising ethanol, ethylacetate and water, removing water from at least a portion of theoverhead vapor to yield an ethanol mixture stream having a lower watercontent than the at least a portion of the overhead vapor, andseparating at least a portion of the ethanol mixture stream in a thirddistillation column to yield a third distillate comprising ethyl acetateand a third residue comprising ethanol and less than 8 wt. % water,e.g., less than 3 wt. % water or less than 0.5 wt. % water.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, wherein like numeralsdesignate similar parts.

FIG. 1 is a schematic diagram of an ethanol production system withsecondary reactor for reducing unreacted acetic acid and with multipledistillation columns to recover ethanol including an acid column andwater separator in accordance with one embodiment of the presentinvention.

FIG. 2 is a schematic diagram of an ethanol production system withsecondary reactor for reducing unreacted acetic acid and with multipledistillation columns having an extractive distillation for recoveringethanol from a stream being recycled to the reactor in accordance withone embodiment of the present invention.

FIG. 3 is a schematic diagram of an ethanol production system withsecondary reactor for reducing unreacted acetic acid and with multipledistillation columns having an extractive distillation for recoveringethanol from a stream being recycled to the initial column in accordancewith one embodiment of the present invention.

FIG. 4 is a schematic diagram of an ethanol production system withsecondary reactor for reducing unreacted acetic acid and with multipledistillation columns to recover ethanol from a stream that comprisesacetic acid and low concentrations of ethyl acetate in accordance withone embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to processes for recovering ethanolproduced by hydrogenating acetic acid in the presence of a catalyst. Thehydrogenation reaction produces a crude ethanol product that comprisesethanol, water, ethyl acetate, acetaldehyde, acetic acid, and otherimpurities. In preferred embodiments, light components such as residualhydrogen are removed from the crude ethanol product as a vapor stream.The concentration of unreacted acetic acid and acetal in the crudeethanol product mixture can vary depending on conditions during thehydrogenation reaction. Separating these compounds from the crudereaction mixture requires additional energy.

In one embodiment, the present invention includes a step of esterifyingunreacted acetic acid contained in the crude ethanol product to reducethe concentration of the unreacted acetic acid, and thus increase thetotal conversion of acetic acid. In this manner, since less acetic acidwill be contained the resulting crude ethanol composition, the energyrequirements for ethanol recovery may be advantageously reduced.

Thus, in processes according to the present invention, the crude ethanolproduct, optionally after removal of the vapor stream discussed above,is esterified in a secondary reactor. In another embodiment, a majorityof the water is removed from the liquid stream prior to esterification.

The secondary reactor may also, in some optional embodiments, hydrolysisimpurities such as diethyl acetal (DEA). Optionally, the process mayinclude a step of reducing the concentration of acetals, such as diethylacetal, in the crude ethanol product though hydrolysis. DEA hydrolyzesto form ethanol which may also improve ethanol production. In thismanner, since less diethyl acetal will be contained the resulting crudeethanol composition, the energy requirements for ethanol recovery may beadvantageously reduced.

The processes of the present invention can also involve separating thecrude ethanol product after the esterification and/or optionalhydrolysis in a first column into a residue stream comprising ethanol,water, ethyl acetate and acetic acid and a distillate stream comprisingacetaldehyde and ethyl acetate. The first column primarily removes lightorganics in the distillate and returns those organics for subsequenthydrogenation. Subsequently, the ethanol is removed from the residuestream to yield an ethanol product. Advantageously, this separationapproach results in reducing energy requirements to recover ethanol, inparticular anhydrous ethanol for fuel grade ethanol, from the crudeethanol product.

The location of the secondary reactor may vary depending on whetheresterification and/or hydrolysis is desired. In one embodiment, bothesterification and hydrolysis may occur in the same secondary reactor.In addition, there may be multiple secondary reactors for esterificationand/or hydrolysis. The secondary reactors may be located prior to thefirst column or in the residue stream between the first and secondcolumn.

In one embodiment of the present invention, the first column can containa side car reactor for esterification of unreacted acetic acid. Thisside car reactor comprises a reactor attached to the column which drawsa feed, either vapor or liquid, from the column and returns it to thecolumn after the feed passes through the side car reactor. The side carreactor is preferably located towards the middle of the column, but feedto the side car reactor may be taken below the feed. By preferablyhaving the side car reactor below the feed during esterification, theresidue stream does not become contaminated with unreacted acetic acid.This side car reactor can be in addition to the other secondaryreactors.

In another embodiment of the present invention, the first column cancontain an integrated reactor on the bottom of the first column as partof the column reboiler loop for esterification of unreacted acetic acid.The vapor return is fed to a secondary reactor, either esterificationand/or hydrolysis, and returned to the column. This integrated reactorcan be in addition to the other secondary reactors.

In recovering ethanol, the processes of the present invention use one ormore distillation columns. In preferred embodiments, the residue streamfrom in the initial column, e.g., first column, comprises a substantialportion of the ethanol, water and acetic acid from the crude ethanolproduct. The residue stream, for example, may comprise at least 50% ofthe ethanol from the crude ethanol product, and more preferably at least70% or at least 90%. In terms of ranges, the residue stream may comprisefrom 50% to 99.9% of the ethanol from the crude ethanol product, andmore preferably from 70% to 99%. Preferably, the amount of ethanol fromthe crude ethanol product recovered in the residue may be greater than97.5%, e.g. greater than 99%.

In another embodiment of the present invention, the residue stream fromthe first column can be sent to a secondary reactor for esterificationof unreacted acetic acid, if present. This esterification can be inaddition to the other secondary reactors. Advantageously, in embodimentsof the present invention utilizing some or more of the esterificationand/or hydrolysis reactors described, improved efficiencies may berealized in recovering ethanol product from the distillation zone,because it is unnecessary to remove residual acetic acid or acetal, or,if residual acetic acid or acetal is present, less energy is required toremove the residuals because of their reduced concentration.

Depending on the ethyl acetate concentration in the residue and whetherthere is in situ esterification in the residue or a secondaryesterification reactor(s) as described above, it may be necessary tofurther separate the ethyl acetate and ethanol in a separate column.Preferably, this separate column is located after the water has beenremoved using a distillation column and water separator. Generally, aseparate column may be necessary when the residue comprises at least 50wppm ethyl acetate or there is esterification. When the ethyl acetate isless than 50 wppm it may not be necessary to use separate column toseparate ethyl acetate and ethanol.

In preferred embodiments, the residue stream from the first columncomprises a substantial portion of the water and the acetic acid, to theextent it has not been esterified, from the crude ethanol product. Theresidue stream may comprise at least 80% of the water from the crudeethanol product, and more preferably at least 90%. In terms of ranges,the residue stream preferably comprises from 80% to 100% of the waterfrom the crude ethanol product, and more preferably from 90% to 99.4%.The residue stream may comprise at least 85% of the acetic acid from thecrude ethanol product, to the extent it has not been esterified, e.g.,at least 90% and more preferably about 100%. In terms of ranges, theresidue stream preferably comprises from 85% to 100% of the acetic acidfrom the crude ethanol product that has not been esterified, and morepreferably from 90% to 100%. In one embodiment, substantially all of theacetic acid that has not been esterified is recovered in the residuestream.

The residue stream comprising ethanol, ethyl acetate, water, and anyremaining acetic acid that has not been esterified may be furtherseparated to recover ethanol. Because these compounds may not be inequilibrium, additional ethyl acetate may be produced through furtheresterification of ethanol and acetic acid. In one preferred embodiment,the water and acetic acid may be removed as another residue stream in aseparate distillation column. In addition, the water carried over in theseparate distillation column may be removed with a water separator thatis selected from the group consisting of an adsorption unit, membrane,extractive column distillation, molecular sieves, and combinationsthereof.

In one embodiment each of the columns is sized to be capital andeconomically feasible for the rate of ethanol production. The totaldiameter for the columns used to separate the crude ethanol product maybe from 5 to 40 meters, e.g., from 10 to 30 meters or from 12 to 20meters. Each column may have a varying size. In one embodiment, theratio of column diameter in meters for all the distillation columns totons of ethanol produced per hour is from 1:2 to 1:30, e.g., from 1:3 to1:20 or from 1:4 to 1:10. This would allow the process to achieveproduction rates of 25 to 250 tons of ethanol per hour.

The distillate from the initial column comprises light organics, such asacetaldehyde, diethyl acetal (to the extent it has not been hydrolyzed),acetone, and ethyl acetate. In addition, minor amounts of ethanol andwater may be present in the distillate. Removing this component from thecrude ethanol product in the initial column provides an efficient meansfor removing acetaldehyde and ethyl acetate. In addition, acetaldehyde,diethyl acetal, and acetone are not carried over with the ethanol whenmultiple columns are used, thus reducing the formation of byproductsfrom acetaldehyde, diethyl acetal, and acetone. In particular,acetaldehyde and/or ethyl acetate may be returned to the reactor, andconverted to additional ethanol. In another embodiment, a purge mayremove these light organics from the system.

The residue from the initial column comprises ethyl acetate. Althoughethyl acetate is also partially withdrawn into the first distillate, ahigher ethyl acetate concentration in the first residue leads toincreased ethanol concentration in the first residue and decreaseethanol concentrations in the first distillate. Thus overall ethanolrecovery may be increased. Ethyl acetate may be separated from ethanolin a separate column near the end of the purification process. Inremoving ethyl acetate, additional light organics may also be removedand thus improve the quality of the ethanol product by decreasingimpurities. Preferably, water and/or acetic acid may be removed prior tothe ethyl acetate/ethanol separation.

In one embodiment, after the ethyl acetate is separated from ethanol,the ethyl acetate is returned to the initial column and fed near the topof that column. This allows for any ethanol removed with the ethylacetate to be recovered and further reduces the amount of ethanol beingrecycled to the reactor. Decreasing the amount of ethanol recycled tothe reactor may reduce reactor capital and improve efficiency inrecovering ethanol. Preferably, the ethyl acetate is removed in thedistillate of the first column and returned to the reactor with theacetaldehyde.

The process of the present invention may be used with any hydrogenationprocess for producing ethanol. The materials, catalysts, reactionconditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethane oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosuresof which are incorporated herein by reference. Optionally, theproduction of ethanol may be integrated with such methanol carbonylationprocesses.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from other carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from other available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from a variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

Biomass-derived syngas has a detectable ¹⁴C isotope content as comparedto fossil fuels such as coal or natural gas. An equilibrium forms in theEarth's atmosphere between constant new formation and constantdegradation, and so the proportion of the ¹⁴C nuclei in the carbon inthe atmosphere on Earth is constant over long periods. The samedistribution ratio n¹⁴C:n¹²C ratio is established in living organisms asis present in the surrounding atmosphere, which stops at death and ¹⁴Cdecomposes at a half life of about 6000 years. Methanol, acetic acidand/or ethanol formed from biomass-derived syngas would be expected tohave a ¹⁴C content that is substantially similar to living organisms.For example, the ¹⁴C:¹²C ratio of the methanol, acetic acid and/orethanol may be from one half to about 1 of the ¹⁴C:¹²C ratio for livingorganisms. In other embodiments, the syngas, methanol, acetic acidand/or ethanol described herein are derived wholly from fossil fuels,i.e. carbon sources produced over 60,000 years ago, may have nodetectable ¹⁴C content.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally, in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. No. 6,509,180, and U.S.Pub. Nos. 2008/0193989 and 2009/0281354, the entireties of which areincorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. Another biomass source is black liquor, which is anaqueous solution of lignin residues, hemicellulose, and inorganicchemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by converting carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form syngas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into syngas, and U.S. Pat.No. 6,685,754, which discloses a method for the production of ahydrogen-containing gas composition, such as a syngas including hydrogenand carbon monoxide, are incorporated herein by reference in theirentireties.

Acetic acid fed to the hydrogenation reactor may also comprise othercarboxylic acids and anhydrides, as well as acetaldehyde and acetone.Preferably, a suitable acetic acid feed stream comprises one or more ofthe compounds selected from the group consisting of acetic acid, aceticanhydride, acetaldehyde, ethyl acetate, and mixtures thereof. Theseother compounds may also be hydrogenated in the processes of the presentinvention. In some embodiments, the presence of carboxylic acids, suchas propanoic acid or its aldehyde, may be beneficial in producingpropanol. Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed, or a series of reactors may be employed with or withoutheat exchange, quenching, or introduction of additional feed material.Alternatively, a shell and tube reactor provided with a heat transfermedium may be used. In many cases, the reaction zone may be housed in asingle vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 10 kPato 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 2100 kPa.The reactants may be fed to the reactor at a gas hourly space velocity(GHSV) from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to 30,000 hr⁻¹,from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 18:1 to 2:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,from 0.1 to 100 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Exemplary catalysts arefurther described in U.S. Pat. Nos. 7,608,744 and 7,863,489, and U.S.Pub. Nos. 2010/0121114 and 2010/0197985, the entireties of which areincorporated herein by reference. In another embodiment, the catalystcomprises a Co/Mo/S catalyst of the type described in U.S. Pub. No.2009/0069609, the entirety of which is incorporated herein by reference.In some embodiments, the catalyst may be a bulk catalyst.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to7.5 wt. %.

Preferred metal combinations for exemplary catalyst compositions includeplatinum/tin, platinum/ruthenium, platinum/rhenium, palladium/ruthenium,palladium/rhenium, cobalt/palladium, cobalt/platinum, cobalt/chromium,cobalt/ruthenium, cobalt/tin, silver/palladium, copper/palladium,copper/zinc, nickel/palladium, gold/palladium, ruthenium/rhenium, orruthenium/iron.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. When present, the total weight of the third metalpreferably is from 0.05 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from0.1 to 7.5 wt. %. In one embodiment, the catalyst may comprise platinum,tin and cobalt.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material. The total weight of the support ormodified support, based on the total weight of the catalyst, preferablyis from 75 to 99.9 wt. %, e.g., from 78 to 99 wt. %, or from 80 to 97.5wt. %. Preferred supports include silicaceous supports, such as silica,silica/alumina, a Group IIA silicate such as calcium metasilicate,pyrogenic silica, high purity silica, and mixtures thereof. Othersupports may include, but are not limited to, iron oxide, alumina,titania, zirconia, magnesium oxide, carbon, graphite, high surface areagraphitized carbon, activated carbons, and mixtures thereof.

The support may be a modified support and the support modifier ispresent in an amount from 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %,from 1 to 20 wt. %, or from 3 to 15 wt. %, based on the total weight ofthe catalyst. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, Sb₂O₃, WO₃, MoO₃, Fe₂O₃, Cr₂O₃, V₂O₅, MnO₂, CuO,Co₂O₃, and Bi₂O₃. Preferred support modifiers include oxides oftungsten, molybdenum, and vanadium.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Thebasic support modifier may be selected from the group consisting ofoxides and metasilicates of any of sodium, potassium, magnesium,calcium, scandium, yttrium, and zinc, as well as mixtures of any of theforegoing. In one embodiment, the basic support modifier is a calciumsilicate, such as calcium metasilicate (CaSiO₃). The calciummetasilicate may be crystalline or amorphous.

Catalysts on a modified support may include one or more metals selectedfrom the group consisting of platinum, palladium, cobalt, tin, andrhenium on a silica support, optionally modified by one or moremodifiers selected from the group consisting of calcium metasilicate,and one or more oxides of tungsten, molybdenum, and/or vanadium.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

After the washing, drying and calcining of the catalyst is completed,the catalyst may be reduced in order to activate the catalyst. Reductionis carried out in the presence of a reducing gas, preferably hydrogen.The reducing gas is continuously passed over the catalyst at an initialambient temperature that is increased up to 400° C. In one embodiment,the reduction is preferably carried out after the catalyst has beenloaded into the reaction vessel where the hydrogenation will be carriedout.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a percentagebased on acetic acid in the feed. The conversion may be at least 40%,e.g., at least 50%, at least 60%, at least 70% or at least 80%. Althoughcatalysts that have high conversions are desirable, such as at least 80%or at least 90%, in some embodiments a low conversion may be acceptableat high selectivity for ethanol.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 60 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 60%.Preferably, the catalyst selectivity to ethanol is at least 60%, e.g.,at least 70%, or at least 80%. Preferred embodiments of thehydrogenation process also have low selectivity to undesirable products,such as methane, ethane, and carbon dioxide. The selectivity to theseundesirable products preferably is less than 4%, e.g., less than 2% orless than 1%.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. The productivity may rangefrom 100 to 3,000 grams of ethanol per kilogram of catalyst per hour.

In various embodiments of the present invention, the crude ethanolproduct produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseacetic acid, ethanol and water. Exemplary compositional ranges for thecrude ethanol product are provided in Table 1, excluding hydrogen. The“others” identified in Table 1 may include, for example, esters, ethers,aldehydes, ketones, alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol  5 to 72 15 to 72 15to 70 25 to 65 Acetic Acid  0 to 90  0 to 50  0 to 35  0 to 15 Water  5to 40  5 to 30 10 to 30 10 to 26 Ethyl Acetate  0 to 30  1 to 25  3 to20  5 to 18 Acetaldehyde  0 to 10 0 to 3 0.1 to 3   0.2 to 2   Others0.1 to 10  0.1 to 6   0.1 to 4   —

In one embodiment, the crude ethanol product of Table 1 may have lowconcentrations of acetic acid with higher conversion, and the aceticacid concentration may range from 0.1 wt. % to 20 wt. %, e.g., 0.2 wt. %to 15 wt. %, from 0.5 wt. % to 10 wt. % or from 1 wt. % to 5 wt. %. Inembodiments having lower amounts of acetic acid, the conversion ofacetic acid is preferably greater than 75%, e.g., greater than 85% orgreater than 90%. In addition, the selectivity to ethanol may also bepreferably high, and is preferably greater than 75%, e.g., greater than85% or greater than 90%.

Exemplary ethanol recovery systems in accordance with embodiments of thepresent invention are shown in FIGS. 1-4. Each hydrogenation system 100provides a suitable hydrogenation reactor and a process for separatingethanol from the crude reaction mixture according to an embodiment ofthe invention. System 100 comprises reaction zone 101 and separationzone 102. FIGS. 1-4 also include one or more secondary reactors in theseparation zone 102. It should be understood that embodiments of thepresent invention may include one of the secondary reactors. Secondaryreactors may each operate in a similar manner and may be in the liquidor vapor phase.

As shown in FIGS. 1-4, the feed to reactor 103 comprises fresh aceticacid. Hydrogen and acetic acid are fed to vaporizer 104 via lines 105and 106, respectively, to create a vapor feed stream in line 107 that isdirected to reactor 103. In one embodiment, lines 105 and 106 may becombined and jointly fed to the vaporizer 104. The temperature of thevapor feed stream in line 107 is preferably from 100° C. to 350° C.,e.g., from 120° C. to 310° C. or from 150° C. to 300° C. Any feed thatis not vaporized is removed from vaporizer 104, via blowdown 108. Inaddition, although line 107 is shown as being directed to the top ofreactor 103, line 107 may be directed to the side, upper portion, orbottom of reactor 103.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe carboxylic acid, preferably acetic acid. In one embodiment, one ormore guard beds (not shown) may be used upstream of the reactor,optionally upstream of vaporizer 104, to protect the catalyst frompoisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials may include, for example,carbon, silica, alumina, ceramic, or resins. In one aspect, the guardbed media is functionalized, e.g., silver functionalized, to trapparticular species such as sulfur or halogens. During the hydrogenationprocess, a crude ethanol product is withdrawn, preferably continuously,from reactor 103 via line 109.

The crude ethanol product may be condensed and fed to a separator 110,which, in turn, forms a vapor stream 112 and a liquid stream 113. Insome embodiments, separator 110 may comprise a flasher or a knockoutpot. Separator 110 may operate at a temperature from 20° C. to 350° C.,e.g., from 30° C. to 325° C. or from 60° C. to 250° C. The pressure ofseparator 106 may be from 50 kPa to 2500 kPa, e.g., from 75 kPa to 2250kPa or from 100 kPa to 2100 kPa. Optionally, the crude ethanol productin line 109 may pass through one or more membranes to separate hydrogenand/or other non-condensable gases.

Vapor stream 112 exiting separator 110 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101. Asshown, vapor stream 112 is combined with the hydrogen feed 105 andco-fed to vaporizer 104. In some embodiments, the returned vapor stream112 may be compressed before being combined with hydrogen feed 105.

In one embodiment, liquid stream 113 from separator 110 can be fed to afirst secondary reactor 111. First secondary reactor 111 preferablyesterifies acetic acid in the liquid stream 113, and may hydrolyze DEAin the liquid stream 113. In one embodiment, it is preferred to esterifyacetic acid in first secondary reactor 111. First secondary reactor 111may be carried out in the liquid or vapor phase. During theesterification, unreacted acetic acid in reactor 111 preferably reactswith ethanol to form ethyl acetate, thus yielding a stream 114 that isester enriched. The ethanol is preferred ethanol produced in reactor 103or may be ethanol obtained from a separate source. Stream 114 comprisesmore ethyl acetate than liquid stream 113, e.g., at least 5 wt. % moreethyl acetate, at least 10 wt. % more ethyl acetate, or at least 20 wt.% more ethyl acetate, based on the weight of ethyl acetate in stream113. In addition, stream 114 preferably comprises less acetic acid thanliquid stream 113. In one embodiment, stream 114 comprises less than 10wt. % unreacted acetic acid based on the total amount of stream 114,e.g., less than 5 wt. % or less than 1 wt. %. In terms of ranges, stream114 may comprise from 0.01 to 10 wt. % unreacted acetic acid, e.g., from0.05 to 5 wt. %, or from 0.05 to 1 wt. %. As a result of esterification,the total conversion of acetic acid in both reactors 103 and 111, may begreater than 90%, e.g., greater than 95% or greater than 99%.

Acid-catalyzed esterification reactions may be used with someembodiments of the present invention. The catalyst should be thermallystable at reaction temperatures. Suitable catalysts for esterificationmay be solid acid catalysts comprising an ion exchange resin, zeolites,Lewis acid, metal oxides, inorganic salts and hydrates thereof,heteropoly acids, and salts thereof. Silica gel, aluminum oxide, andaluminum phosphate are also suitable catalysts. Acid catalysts include,but are not limited to, sulfuric acid, and tosic acid. In addition,Lewis acids may also be used as esterification catalysts, such asscandium(III) or lanthanide(III) triflates, hafnium(IV) or zirconium(IV)salts, and diarylammonium arenesulfonates. The catalyst may also includesulfonated (sulphonic acid) ion-exchange resins (e.g., gel-type andmacroporous sulfonated styrene-divinyl benzene IERs), sulfonatedpolysiloxane resins, sulfonated perfluorinated (e.g., sulfonatedpoly-perfluoroethylene), or sulfonated zirconia.

Embodiments of the present invention reduce unreacted acetic acidconcentration without a large penalty to overall ethanol yields.Preferably, the unreacted acetic acid concentration is reduced fromliquid stream 113 to stream 114 by at least 40%, e.g., at least 50%, atleast 75%, or at least 85%. These reductions, however, are coupled witha minor penalty in ethanol production. Preferably, overall ethanolproduction is reduced by less than 10%, e.g., less than 5%, or less than2% relative to the same system but without an esterification unit.Although larger ethanol reductions may be possible, it is generally notdesired to reduce unreacted acid concentrations at the expense ofsignificant ethanol reductions.

In first secondary reactor 111, DEA may also be hydrolyzed in additionthe esterification of acetic acid. The water co-produced in thehydrogenation reaction may be used to hydrolyze the DEA or water from anexternal source may be used. It is more preferred to use waterco-produced that is either in liquid stream 113 or recycled separationzone 102. During the hydrolysis DEA forms a stream comprising ethanoland an aldehyde, thus yielding a stream 114 with reduced acetalconcentration. Stream 114 has less acetal than liquid steam 113.Although acetal may be hydrolyzed in the absence of a catalyst, it is apreferred that a catalyst is employed to increase reaction rate. Apreferred pH for the hydrolysis is less than 6, more preferred is lessthan 5, and most preferred is a pH less than 4. In a preferredembodiment, this can be an acid catalyst, such as acetic acid orphosphoric acid or a sulfonic resin bed. According to one embodiment ofthe invention, liquid stream 113 is passed through first secondaryreactor 111 comprising an ion exchange resin reactor bed. The ionexchange resin reactor bed may comprise a strongly acidic heterogeneousor homogenous catalyst, such as for example a Lewis acid, stronglyacidic ion exchange catalyst, inorganic acids, and methanesulfonic acid.Exemplary catalysts include Amberlyst™ 15 (Rohm and Haas Company,Philadelphia, U.S.A.), Amberlyst™ 70, Dowex-M-31 (Dow Chemical Company),Dowex Monosphere M-31 (Dow Chemical Company), and Purolite CT typeCatalysts (Purolite International SRL). The ion exchange resin reactorbed preferably is a gel or marco-reticular bed.

In one embodiment, first secondary reactor 111 may hydrolyze DEA andesterify acetic acid to produce a stream 114 that is ester enriched andhas a reduced acetal concentration. The catalyst for both esterificationand hydrolysis may be the same.

When stream 114 is produced by first secondary reactor 111, it may befed to first column 115 as described below.

Liquid stream 113, or optionally stream 114, is directed as a feedcomposition to the side of first distillation column 115, also referredto as an “extractive column.” Liquid stream 113 may be heated fromambient temperature to a temperature of up to 70° C., e.g., up to 50°C., or up to 40° C. The additional energy required to pre-heat liquidstream 113 above 70° C. does not achieve the desired energy efficiencyin first column 115 with respect to reboiler duties. In anotherembodiment, liquid stream 113 is not separately preheated, but is fed tofirst column 115 at a temperature of less than 70° C., e.g., less than50° C., or less than 40° C.

In one embodiment, the contents of liquid stream 113 are substantiallysimilar to the crude ethanol product obtained from the reactor, exceptthat the composition has been depleted of hydrogen, carbon dioxide,methane or ethane, which have been removed by separator 110.Accordingly, liquid stream 113 may also be referred to as a crudeethanol product. Exemplary components of liquid stream 113 are providedin Table 2, without secondary reactor 111. When secondary reactor 111 isused, the acetic acid and diethyl acetal may vary as described above. Itshould be understood that liquid stream 113 may contain othercomponents, not listed in Table 2.

TABLE 2 FEED COMPOSITION TO COLUMN 115 (Liquid Stream 113) Conc. (wt. %)Conc. (wt. %) Conc. (wt. %) Ethanol 5 to 72 10 to 70 15 to 65 AceticAcid <90  5 to 80  0 to 35 Water 5 to 40  5 to 30 10 to 26 Ethyl Acetate<30  1 to 25  3 to 20 Acetaldehyde <10 0.001 to 3    0.1 to 3   DiethylAcetal  <5 0.01 to 5   0.01 to 3   Acetone  <5 0.0005 to 0.05  0.001 to0.03 

The amounts indicated as less than (<) in the tables throughout thepresent specification are preferably not present and if present may bepresent in amounts greater than 0.0001 wt. %.

In one embodiment, the ethyl acetate concentration in the liquid stream113 may affect the first column reboiler duty and size. Decreasing ethylacetate concentrations may allow for reduced reboiler duty and size. Inone embodiment, to reduce the ethyl acetate concentration (a) thecatalyst in reactor may convert ethyl acetate in addition to aceticacid; (b) the catalyst may be less selective for ethyl acetate, and/or(c) the feed to reactor, including recycles, may contain less ethylacetate.

In the embodiment shown in FIG. 1, liquid stream 113 is introduced inthe upper part of first column 115, e.g., upper half or upper third. Inaddition to liquid stream 113, an extractive agent 116 and an ethylacetate recycle stream 117 are also fed to first column. Extractiveagent 116 is preferably introduced above the liquid stream 113.Extractive agent 116 may be heated from ambient temperature to atemperature of up to 70° C., e.g., up to 50° C., or up to 40° C. Inanother embodiment, extractive agent 116 is not separately preheated,but is withdrawn from second column 130, and cooled, if necessary, to atemperature of less than 70° C., e.g., less than 50° C., or less than40° C., and directly fed to first column 115. Depending on the ethylacetate concentration of ethyl acetate recycle stream 117 this streammay be introduced above or near the feed point of the liquid stream 113.Depending on the targeted ethyl acetate concentration in the distillateof first column 115 the feed point of ethyl acetate recycle stream 117will vary.

Liquid stream 113 and ethyl acetate recycle stream 117 collectivelycomprise the organic feed to first column 115. In one embodiment,organic feed comprises from 1 to 25% of ethyl acetate recycle stream117, e.g., from 1% to 15% or from 1% to 10%. The relative amounts mayvary depending on the production of reactor 103, whether unreactedacetic acid is esterified, and/or the amount of ethyl acetate to berecycled.

Extractive agent 116 preferably comprises water that has been retainedwithin the system. As described herein, extractive agent 116 may beobtained from a portion of the second residue. Extractive agent 116 maybe a dilute acid stream comprising up to 20 wt. % acetic acid, e.g., upto 10 wt. % acetic acid or up to 5 wt. % acetic acid. In one embodiment,the mass flow ratio of water in extractive agent 116 to the mass flow ofthe organic feed, which comprises liquid stream 113 and ethyl acetaterecycle stream 117, may range from 0.05:1 to 2:1, e.g., from 0.07 to0.9:1 or from 0.1:1 to 0.7:1. It is preferred that the mass flow ofextractive agent 116 is less than the organic feed.

In one embodiment, first column 115 is a tray column having from 5 to 90theoretical trays, e.g. from 10 to 60 theoretical trays or from 15 to 50theoretical trays. The number of actual trays for each column may varydepending on the tray efficiency, which is typically from 0.5 to 0.7depending on the type of tray. The trays may be sieve trays, fixed valvetrays, movable valve trays, or any other suitable design known in theart. In other embodiments, a packed column having structured packing orrandom packing may be employed.

When first column 115 is operated under 50 kPa, the temperature of theresidue exiting in line 118 preferably is from 20° C. to 100° C., e.g.,from 30° C. to 90° C. or from 40° C. to 80° C. The base of column 115may be maintained at a relatively low temperature by withdrawing aresidue stream comprising ethanol, ethyl acetate, water, and aceticacid, thereby providing an energy efficiency advantage. The temperatureof the distillate exiting in line 119 from column 115 preferably at 50kPa is from 10° C. to 80° C., e.g., from 20° C. to 70° C. or from 30° C.to 60° C. The pressure of first column 115 may range from 0.1 kPa to 510kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In someembodiments, first column 115 may operate under a vacuum of less than 70kPa, e.g., less than 50 kPa, or less than 20 kPa. Operating under avacuum may decrease the reboiler duty and reflux ratio of first column115. However, a decrease in operating pressure for first column 115 doesnot substantially affect column diameter.

In some embodiments, first column 115 may contain a second secondaryreactor 122 for esterification of acetic acid and/or hydrolysis ofacetal. Second secondary reactor 122, which may also be referred to as aside car reactor, and may be used in addition with the other secondaryreactors described herein or alone. The pH in the side car reactor maybe less than 6. Second secondary reactor 122 receives a liquid or vaporside draw in line 153 from first column 115. Side draw in line 153location may vary. Preferably, side draw in line 153 is taken near themiddle of first column 115, but below the feed for liquid stream 113 sothat acetic acid and/or acetal do not contaminate the residue stream 118from column 115. For similar reasons, it is also preferred that the feedto the second secondary reactor 122 from a point lower on column 115than the point on column 115 to which the reaction product in line 154of the second secondary reactor 122 is returned.

Second secondary reactor 122 may function under similar conditions asfirst secondary reactor 111, both in terms of the esterification ofacetic acid and/or in terms of the hydrolysis of DEA. In one embodiment,acetic acid may be esterified in second secondary reactor 122.

In some embodiments, first column 115 may contain a third secondaryreactor 152 for esterification of acetic acid and/or hydrolysis of DEApresent in the reboiler stream 155 of first column 115. Third secondaryreactor 152 may be referred to as an integrated reboiler reactor and maybe used in addition with the other secondary reactors described hereinor alone. Third secondary reactor 152 is located in the reboiler loop155 of first column 115. The reaction products 156 that are formed as aresult of the esterification/hydrolysis in the integrated reboilerreactor drive the column as vapor return in line 156. Thus, it ispreferred to operate third secondary reactor 152 in the vapor phase.

Third secondary reactor 122 may function under similar conditions asfirst or second secondary reactors, both in terms of the esterificationof acetic acid and/or in terms of the hydrolysis of DEA.

In first column 115, a weight majority of the ethanol, water, aceticacid, are removed from the organic feed, including liquid stream 113 andethyl acetate recycle stream 117, and are withdrawn, preferablycontinuously, as residue in line 118. This includes any water added asan extractive agent 116, as well as ethanol formed from the hydrolysisof diethyl acetal. Concentrating the ethanol in the residue reduces theamount of ethanol that is recycled to reactor 103 and in turn reducesthe size of reactor 103. Preferably less than 10% of the ethanol fromthe organic feed, e.g., less than 5% or less than 1% of the ethanol, isreturned to reactor 103 from first column 115. In addition,concentrating the ethanol also will concentrate the water and/or aceticacid in the residue. In one embodiment, at least 90% of the ethanol fromthe organic feed is withdrawn in the residue, and more preferably atleast 95%. In addition, ethyl acetate may also be present in the firstresidue in line 118. The reboiler duty may decrease with an ethylacetate concentration increase in the first residue in line 118.

First column 115 also forms a distillate, which is withdrawn in line119, and which may be condensed and refluxed, for example, at a ratiofrom 30:1 to 1:30, e.g., from 10:1 to 1:10 or from 5:1 to 1:5. Highermass flow ratios of water to organic feed may allow first column 115 tooperate with a reduced reflux ratio.

First distillate in line 119 preferably comprises a weight majority ofthe acetaldehyde and ethyl acetate from liquid stream 114, as well asfrom ethyl acetate recycle stream 117 and acetaldehyde and ethyl acetateformed from hydrolysis or esterification, respectively, as describedabove. In one embodiment, the first distillate in line 119 comprises aconcentration of ethyl acetate that is less than the ethyl acetateconcentration for the azeotrope of ethyl acetate and water, and morepreferably less than 75 wt. %.

In some embodiments, first distillate in line 119 also comprisesethanol. Returning the ethanol may require an increase in reactorcapacity to maintain the same level of ethanol efficiency. To recoverethanol, first distillate in line 119 is fed, as is shown in FIG. 2, toan extraction column 120 to recover ethanol and reduce the ethanolconcentration recycled to reactor 103. Extraction column 120 may be amulti-stage extractor. In extraction column 120, the first distillate inline 119 is fed along with at least one extractant 121. In oneembodiment, extractant 121 may be benzene, propylene glycol, andcyclohexane. Although water may be used, the extractant 121 preferablydoes not form an azeotrope with ethanol. A suitable extractant 121 ispreferably non-carcinogenic and non-hazardous. Preferably, theextractant extracts ethanol from the first distillate in extract stream122. The extractant may be recovered in recovery column 123 and returnedvia line 124. The ethanol stream in line 125 may be combined withethanol product or returned to one of the distillation columns, such asfirst column 115. Raffinate 126 may be returned to reaction zone 101.Preferably, raffinate 126, which comprises acetaldehyde and ethylacetate, is deficient in ethanol with respect to first distillate inline 119.

Exemplary components of the distillate and residue compositions forfirst column 115 are provided in Table 3 below. It should also beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 3. Acetic acid and DEA concentration mayvary if one or more of the secondary reactors are used as describedabove. For convenience, the distillate and residue of the first columnmay also be referred to as the “first distillate” or “first residue.”The distillates or residues of the other columns may also be referred towith similar numeric modifiers (second, third, etc.) in order todistinguish them from one another, but such modifiers should not beconstrued as requiring any particular separation order.

TABLE 3 FIRST COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethyl Acetate 10 to 85 15 to 80 20 to 75 Acetaldehyde 0.1 to70  0.2 to 65  0.5 to 65  Diethyl Acetal   <3 0.01 to 2   0.05 to 1.5 Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Ethanol   <25 0.001 to 20  0.01 to 15   Water 0.1 to 20   1 to 15  2 to 10 Acetic Acid   <2 <0.1<0.05 Residue Acetic Acid 0.1 to 50  0.5 to 40   1 to 30 Water 20 to 8525 to 80 30 to 75 Ethanol 10 to 75 15 to 70 20 to 65 Ethyl Acetate 0.005to 30   0.03 to 25   0.08 to 1  

In one embodiment of the present invention, first column 115 may beoperated at a temperature where most of the water, ethanol, and aceticacid are removed into the residue stream and only a small amount ofethanol and water is collected in the distillate stream due to theformation of binary and tertiary azeotropes. The ratio of water in theresidue in line 118 to water in the distillate in line 119 may begreater than 1:1 by weight, e.g., greater than 2:1. The weight ratio ofethanol in the residue to ethanol in the distillate may be greater than1:1 by weight, e.g., greater than 2:1. Thus, more water and/or ethanolis withdrawn in the residue.

The amount of acetic acid in the first residue may vary depending on theconversion in reactor 103 and in secondary reactors 111, 122, and 152.In one embodiment, when the overall conversion is high, e.g., greaterthan 90%, the amount of acetic acid in the first residue may be lessthan 10 wt. %, e.g., less than 5 wt. % or less than 2 wt. %. In otherembodiments, when the conversion is lower, e.g., less than 90%, theamount of acetic acid in the first residue may be greater than 10 wt. %.

The first distillate in line 119 preferably is substantially free ofacetic acid, e.g., comprising less than 1000 wppm, less than 500 wppm orless than 100 wppm acetic acid. The distillate may be purged from thesystem or recycled in whole or part to reactor 103. In some embodiments,when the distillate comprises ethyl acetate and acetaldehyde, thedistillate may be further separated, e.g., in a distillation column (notshown), into an acetaldehyde stream and an ethyl acetate stream. Theethyl acetate stream may also be hydrolyzed or reduced with hydrogen,via hydrogenolysis, to produce ethanol. Either of these streams may bereturned to reactor 103 or separated from system 100 as additionalproducts.

Some species, such as acetals, may decompose in first column 115 or behydrolyzed in secondary reactors 111, 122, and/or 152 such that very lowamounts, or even no detectable amounts, of acetals remain in thedistillate or residue. Preferably the distillate and residue contain noacetal.

In addition, an equilibrium reaction between acetic acid/ethanol andethyl acetate may occur in the crude ethanol product after exitingreactor 103 or first column 115. Without being bound by theory, ethylacetate may be formed in the reboiler of first column 115, even when nothird secondary reactor 152 is used. Depending on the concentration ofacetic acid in the crude ethanol product, this equilibrium may be driventoward formation of ethyl acetate. This reaction may be regulatedthrough the residence time and/or temperature of the crude ethanolproduct.

In one embodiment, due to the composition of first residue in line 118the equilibrium may favor esterification to produce ethyl acetate. Whilethe esterification, either in the liquid or vapor phase, may consumeethanol, the esterification may also reduce the amount of acetic acidthat needs to be removed from the process. Ethyl acetate may be removedfrom first column 115 or formed in situ ethyl acetate via esterificationbetween first column 115 and second column 130. The esterification maybe further promoted by passing a portion of the first residue in line118 through a fourth secondary reactor 127, as shown in FIG. 3. Fourthsecondary reactor 152 may esterify acetic acid and may be used inaddition with the other secondary reactors described herein or alone.Due to the low concentrations of diethyl acetal in first residue in line118, it is not preferred to use a hydrolysis reactor. Fourth secondaryreactor 127 may function under similar conditions as the other reactors,in terms of the esterification of acetic acid.

Fourth secondary reactor 127 may be either a liquid or vapor phasereactor and may comprise an acidic catalyst, as previously described. Avapor phase reactor is preferred to convert some of the first residueinto an intermediate vapor feed 128 to be introduced into the secondcolumn 130, as shown in FIG. 1.

To recover ethanol, first residue in line 118, or intermediate vaporfeed 128, may be further separated depending on the concentration ofacetic acid and/or ethyl acetate. In embodiments of the presentinvention, residue in line 118, or intermediate vapor feed 128 isfurther separated in a second column 130, also referred to as an “acidcolumn.” Second column 130 yields a second residue in line 131comprising acetic acid and water, and a second distillate in line 132comprising ethanol and ethyl acetate. In one embodiment, a weightmajority of the water and/or acetic acid fed to second column 130 isremoved in the second residue in line 131, e.g., at least 60% of thewater and/or acetic acid is removed in the second residue in line 131 ormore preferably at least 80% of the water and/or acetic acid. An acidcolumn may be desirable, for example, when the acetic acid concentrationin the first residue is greater 50 wppm, e.g., greater than 0.1 wt. %,greater than 1 wt. %, e.g., greater than 5 wt. %.

In one embodiment first residue in line 118 may be preheated prior tobeing introduced into second column 130. The first residue in line 118may be heat integrated with either the residue of the second column 130or vapor overhead of second column 130. In some embodiments,esterification and/or hydrolysis may be carried out in the vapor phasein secondary reactor 127 which results in preheating a portion of firstresidue in line 118 to form an intermediate vapor feed 128. For purposesof the present invention, when preheating it is preferred than less than30 mol. % of first residue in line 118 is in the vapor phase, e.g., lessthan 25 mol. % or less than 20 mol. %. Greater vapor phase contentsresult in increased energy consumption and a significant increase in thesize of second column 130. A portion of the first residue in line 129may by-pass the fourth secondary reactor 127 and be combined with theintermediate vapor feed 128 to maintain the necessary vapor molefraction.

Esterifying the acetic acid in first residue in line 118 increases theethyl acetate concentration which leads to increases in the size ofsecond column 130 as well increases in reboiler duty. Thus, theconversion of acetic acid may be controlled depending on the initialethyl acetate concentration withdrawn from first column. To maintain anefficient separation the ethyl acetate concentration of the firstresidue in line 118 feed to second column is preferably less than 1000wppm, e.g., less than 800 wppm or less than 600 wppm.

Second column 130 operates in a manner to concentrate the ethanol fromfirst residue such that a majority of the ethanol is carried overhead.Thus, the residue of second column 130 may have a low ethanolconcentration of less than 5 wt. %, e.g. less than 1 wt. % or less than0.5 wt. %. Lower ethanol concentrations may be achieved withoutsignificant increases in reboiler duty or column size. Thus, in someembodiments it is efficient to reduce the ethanol concentration in theresidue to less than 50 wppm, or more preferably less than 25 wppm. Asdescribed herein, the residue of second column 130 may be treated andlower concentrations of ethanol allow the residue to be treated withoutgenerating further impurities.

In FIG. 1, the first residue in line 118 or the intermediate vapor feed128 is introduced to second column 130 preferably in the top part ofcolumn 130, e.g., top half or top third. Feeding first residue in line118 or intermediate vapor feed 128 in a lower portion of second column130 may unnecessarily increase the energy requirements of second column.Acid column 130 may be a tray column or packed column. In FIG. 1, secondcolumn 130 may be a tray column having from 10 to 110 theoretical trays,e.g. from 15 to 95 theoretical trays or from 20 to 75 theoretical trays.Additional trays may be used if necessary to further reduce the ethanolconcentration in the residue. In one embodiment, the reboiler duty andcolumn size may be reduced by increasing the number of trays.

Although the temperature and pressure of second column 130 may vary,when at atmospheric pressure the temperature of the second residue inline 131 preferably is from 95° C. to 160° C., e.g., from 100° C. to150° C. or from 110° C. to 145° C. In one embodiment, when first residuein line 118 is preheated to a temperature that is within 20° C. of thetemperature of second residue in line 131, e.g., within 15° C. or within10° C. The temperature of the second distillate exiting in line 132 fromsecond column 130 preferably is from 50° C. to 120° C., e.g., from 75°C. to 118° C. or from 80° C. to 115° C. The temperature gradient may besharper in the base of second column 130.

The pressure of second column 130 may range from 0.1 kPa to 510 kPa,e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In one embodiment,second column 130 operates above atmospheric pressure, e.g., above 170kPa or above 375 kPa. Second column 130 may be constructed of a materialsuch as 316L SS, Allot 2205 or Hastelloy C, depending on the operatingpressure. The reboiler duty and column size for second column remainrelatively constant until the ethanol concentration in the seconddistillate in line 132 is greater than 90 wt. %.

As described herein first column 115 is an extractive column thatpreferably uses water. The additional water is separated in secondcolumn 130. While using water as an extractive agent may reduce thereboiler duty of first column 115, when the mass flow ratio of water toorganic feed is larger than 0.65:1, e.g., larger than 0.6:1 or largerthan 0.54:1, the additional water will cause an increase in reboilerduty of second column 130 that offsets any benefit gained by firstcolumn 115.

Second column 130 also forms an overhead, which is withdrawn in line133, and which may be condensed and refluxed, for example, at a ratiofrom 12:1 to 1:12, e.g., from 10:1 to 1:10 or from 8:1 to 1:8. Theoverhead in line 133 preferably comprises 85 to 92 wt. % ethanol, e.g.,about 87 to 90 wt. % ethanol, with the remaining balance being water andethyl acetate.

In one embodiment, water may be removed prior to recovering the ethanolproduct. In one embodiment, the overhead in line 133 may comprise lessthan 15 wt. % water, e.g., less than 10 wt. % water or less than 8 wt. %water. As shown in FIG. 1, overhead vapor in line 133 may be fed towater separator 135, which may be an adsorption unit, membrane,molecular sieves, extractive column distillation, or a combinationthereof. In one embodiment, at least 50% of overhead vapor is fed towater separator 135, e.g., at least 75% or at least 90%. Optionally,some of overhead vapor in line 133 is condensed as second distillate 132and optionally may be fed directly to third distillation column 140.

Water separator 135 in FIG. 1 may be a pressure swing adsorption (PSA)unit. For purposes of clarity the details of the PSA unit are not shownin the figures. The PSA unit is optionally operated at a temperaturefrom 30° C. to 160° C., e.g., from 80° C. to 140° C., and a pressurefrom 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. The PSA unit maycomprise two to five beds. Water separator 135 may remove at least 95%of the water overhead vapor 133, and more preferably from 95% to 99.99%of the water from vapor overhead 133, into a water stream 134. All or aportion of water stream 134 may be returned to second column 130 in line136, which may increase the reboiler duty and/or size of second column130. Additionally or alternatively, all or a portion of water stream maybe purged via line 137. The remaining portion of vapor overhead 133exits the water separator 135 as ethanol mixture stream 138. In oneembodiment, ethanol mixture stream 138 comprises more than 92 wt. %ethanol, e.g., more than 95 wt. % or more than 99 wt. %. In oneembodiment a portion of water stream 137 may be fed to first column 115as the extractive agent.

A portion of vapor overhead 133 may be condensed and refluxed to secondcolumn 130, as shown, for example, at a ratio from 12:1 to 1:12, e.g.,from 10:1 to 1:10 or from 8:1 to 1:8. The second distillate in line 132optionally may be mixed with ethanol mixture stream 138 and co-fed tolight ends column 140. This may be necessary if additional water isneeded to improve separation in light ends column 140. It is understoodthat reflux ratios may vary with the number of stages, feed locations,column efficiency and/or feed composition. Operating with a reflux ratioof greater than 3:1 may be less preferred because more energy may berequired to operate second column 130.

Exemplary components for ethanol mixture stream 138 and residuecompositions for second column 130 are provided in Table 4 below. Itshould be understood that the distillate and residue may also containother components, not listed in Table 4. For example, in optionalembodiments, when ethyl acetate is in the feed to reactor 103, secondresidue in line 131 exemplified in Table 4 may also comprise highboiling point components.

TABLE 4 ACID COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %) EthanolMixture Stream Ethanol   90 to 99.9 92 to 99 96 to 99 Ethyl Acetate <100.001 to 5    0.005 to 4    Acetaldehyde <10 0.001 to 5    0.005 to 4   Water <10 0.001 to 3    0.01 to 1   Acetal  <2 0.001 to 1    0.005 to0.5  Second Residue Acetic Acid 0.1 to 45  0.2 to 40  0.5 to 35  Water 45 to 100   55 to 99.8   65 to 99.5 Ethyl Acetate <0.1 0.0001 to 0.05 0.0001 to 0.01  Ethanol   <5 0.002 to 1    0.005 to 0.5 

The weight ratio of ethanol in the ethanol mixture stream 138 to ethanolin the second residue in line 131 preferably is at least 35:1.Preferably, ethanol mixture stream 138 is substantially free of aceticacid and may contain, if any, trace amounts of acetic acid.

In one embodiment, ethyl acetate fed to second column 130 mayconcentrate in the vapor overhead and pass through with the ethanolmixture stream 138. Thus, preferably no ethyl acetate is withdrawn inthe second residue in line 131. Advantageously this allows most of theethyl acetate to be subsequently recovered without having to furtherprocess the second residue in line 131.

In optional embodiments, the feed to reactor 103 may comprise aceticacid and/or ethyl acetate. When ethyl acetate is used alone as a feed,the crude ethanol product may comprise substantially no water and/oracetic acid. There may be high boiling point components, such asalcohols having more than 2 carbon atoms, e.g., n-propanol, isopropanol,n-butanol, 2-butanol, and mixtures thereof. High boiling pointcomponents refer to compounds having a boiling point that is greaterthan ethanol. The high boiling point components may be removed in secondcolumn 125 in the second residue in line 131 described herein.

In one embodiment, due to the presence of ethyl acetate in ethanolmixture stream 138, an additional third column 140 may be used. A thirdcolumn 140, referred to as a “light ends” column, is used for removingethyl acetate from ethanol mixture stream 138 and producing an ethanolproduct in the third residue in line 141. Light ends column 140 may be atray column or packed column. In FIG. 1, third column 140 may be a traycolumn having from 5 to 90 theoretical trays, e.g. from 10 to 60theoretical trays or from 15 to 50 theoretical trays.

The feed location of ethanol mixture stream 138 may vary depending onethyl acetate concentration and it is preferred to feed ethanol mixturestream 138 to the upper portion of third column 140. Higherconcentrations of ethyl acetate may be fed at a higher location in thirdcolumn 140. The feed location should avoid the very top trays, near thereflux, to avoid excess reboiler duty requirements for the column and anincrease in column size. For example, in a column having 45 actualtrays, the feed location should between 10 to 15 trays from the top.Feeding at a point above this may increase the reboiler duty and size oflight ends column 140.

Ethanol mixture stream 138 may be fed to third column 140 at atemperature of up to 70° C., e.g., up to 50° C., or up to 40° C. In someembodiments it is not necessary to further preheat ethanol mixturestream 138.

Ethyl acetate may be concentrated in the third distillate in line 142.Due to the relatively lower amounts of ethyl acetate fed to third column140, third distillate in line 142 also comprises substantial amounts ofethanol. To recover the ethanol, third distillate in line 142 may be fedto first column as the ethyl acetate recycle stream 117. Because thisincreased the demands on the first and second columns, it is preferredthat the concentration of ethanol in third distillate in line 142 befrom 70 to 90 wt. %, e.g., from 72 to 88 wt. %, or from 75 to 85 wt. %.

In other embodiments, a portion of third distillate in line 142 may bepurged from the system in line 143 as additional products, such as anethyl acetate solvent.

In some embodiments to recover the ethanol without sending thirddistillate in line 142 back to first column 115, the ethanol may berecovered using an extractive column 145 as shown in FIG. 3. Extractioncolumn 145 may be a multi-stage extractor. In extraction column 145, thethird distillate in line 142 is fed along with at least one extractiveagent 146. In one embodiment, the extractive agent may be benzene,propylene glycol, and cyclohexane. Although water may be used, theextractive agent preferably does not form an azeotrope with ethanol. Asuitable extractive agent 146 is preferably non-carcinogenic andnon-hazardous. Preferably, the extractive agent extracts ethanol fromthe third distillate in extractant 147. The extractive agent may berecovered in recovery column 148 and returned via line 149. The ethanolstream in line 150 may be combined with third residue in line 141. Theraffinate 151, which comprises ethyl acetate, may be returned toreaction zone 101 or optionally to first column 115 as ethyl acetaterecycle stream 117. Preferably, raffinate 151 is deficient in ethanolwith respect to third distillate in line 142.

In an optional embodiment, the third residue may be further processed torecover ethanol with a desired amount of water, for example, using afurther distillation column, adsorption unit, membrane or combinationthereof, may be used to further remove water from third residue in line141 as necessary. In most embodiments, the water is removed prior tothird column 140 using water separator 135 and thus further drying ofthe ethanol is not required.

Third column 140 is preferably a tray column as described above andpreferably operates at atmospheric pressure. The temperature of thethird residue in line 141 exiting from third column 140 preferably isfrom 65° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to80° C. The temperature of the third distillate in line 142 exiting fromthird column 140 preferably is from 30° C. to 70° C., e.g., from 40° C.to 65° C. or from 50° C. to 65° C.

The pressure of third column 140 may range from 0.1 kPa to 510 kPa,e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. In someembodiments, third column 140 may operate under a vacuum of less than 70kPa, e.g., less than 50 kPa, or less than 20 kPa. Decreasing inoperating pressure substantially decreases column diameter and reboilerduty for third column 140.

Exemplary components for ethanol mixture stream and residue compositionsfor third column 140 are provided in Table 5 below. It should beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 5.

TABLE 5 LIGHT ENDS COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Third Distillate Ethanol 70 to 90 72 to 88 75 to 85 Ethyl Acetate  1 to30  1 to 25  1 to 15 Acetaldehyde  <15 0.001 to 10   0.1 to 5   Water <10 0.001 to 2    0.01 to 1   Acetal   <2 0.001 to 1    0.01 to 0.5 Third Residue Ethanol   80 to 99.5 85 to 97 90 to 95 Water   <3 0.001 to2    0.01 to 1   Ethyl Acetate <1.5 0.0001 to 1    0.001 to 0.5  AceticAcid <0.5 <0.01 0.0001 to 0.01 

When first residue in line 118 comprise low amounts of acetic acidand/or there is no esterification of first residue, such that the ethylacetate concentration is less than 50 wppm, third column 140 may beoptional and removed as shown in FIG. 4. Thus, ethanol mixture stream138 from the water separator 135 may be the ethanol product and there isno ethyl acetate recycle stream.

Depending on the amount of water and acetic acid contained in the secondresidue in line 131 may be treated in one or more of the followingprocesses. Although some embodiments utilizing theesterification/hydrolysis secondary described may advantageouslyeliminate the need for recovering acetic acid, in some cases there maybe a need for recovery unreacted acetic acid. A suitable weak acidrecovery system is described in US Pub. No. 2012/0010446, the entirecontents and disclosure of which is hereby incorporated by reference.When the residue comprises a majority of acetic acid, e.g., greater than70 wt. %, the residue may be recycled to the reactor without anyseparation of the water. In one embodiment, the residue may be separatedinto an acetic acid stream and a water stream when the residue comprisesa majority of acetic acid, e.g., greater than 50 wt. %. Acetic acid mayalso be recovered in some embodiments from first residue having a loweracetic acid concentration. The residue may be separated into the aceticacid and water streams by a distillation column or one or moremembranes. If a membrane or an array of membranes is employed toseparate the acetic acid from the water, the membrane or array ofmembranes may be selected from any suitable acid resistant membrane thatis capable of removing a permeate water stream. The resulting aceticacid stream optionally is returned to reactor 103. The resulting waterstream may be used as an extractive agent or to hydrolyze an acetalcontaining stream or an ester-containing stream in a hydrolysis unit.

In other embodiments, for example where second residue in line 131comprises less than 50 wt. % acetic acid, possible options include oneor more of: (i) returning a portion of the residue to reactor 103, (ii)neutralizing the acetic acid, (iii) reacting the acetic acid with analcohol, or (iv) disposing of the residue in a waste water treatmentfacility. It also may be possible to separate a residue comprising lessthan 50 wt. % acetic acid using a weak acid recovery distillation columnto which a solvent (optionally acting as an azeotroping agent) may beadded. Exemplary solvents that may be suitable for this purpose includeethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, vinylacetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue in line 131 comprises less than10 wt. % acetic acid. Acetic acid may be neutralized with any suitablealkali or alkaline earth metal base, such as sodium hydroxide orpotassium hydroxide. When reacting acetic acid with an alcohol, it ispreferred that the residue comprises less than 50 wt. % acetic acid. Thealcohol may be any suitable alcohol, such as methanol, ethanol,propanol, butanol, or mixtures thereof. The reaction forms an ester thatmay be integrated with other systems, such as carbonylation productionor an ester production process. Preferably, the alcohol comprisesethanol and the resulting ester comprises ethyl acetate. Optionally, theresulting ester may be fed to the hydrogenation reactor.

In some embodiments, when the residue in line 131 comprises very minoramounts of acetic acid, e.g., less than 5 wt. % or less than 1 wt. %,the residue may be neutralized and/or diluted before being disposed ofto a waste water treatment facility. The organic content, e.g., aceticacid content, of the residue beneficially may be suitable to feedmicroorganisms used in a waste water treatment facility.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary.Temperatures within the various zones will normally range between theboiling points of the composition removed as the distillate and thecomposition removed as the residue. As will be recognized by thoseskilled in the art, the temperature at a given location in an operatingdistillation column is dependent on the composition of the material atthat location and the pressure of column. In addition, feed rates mayvary depending on the size of the production process and, if described,may be generically referred to in terms of feed weight ratios.

The ethanol product produced by the process of the present invention maybe an industrial grade ethanol or fuel grade ethanol. Exemplary finishedethanol compositional ranges are provided below in Table 6.

TABLE 6 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt .%) Conc. (wt.%) Conc. (wt. %) Ethanol   85 to 99.9   90 to 99.5   92 to 99.5 Water<12 0.1 to 9   0.5 to 8   Acetic Acid <1 <0.1  <0.01  Ethyl Acetate <2<0.5  <0.05  Acetal <0.05 <0.01 <0.005 Acetone <0.05 <0.01 <0.005Isopropanol <0.5 <0.1  <0.05  n-propanol <0.5 <0.1  <0.05 

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogen transport or consumption. Infuel applications, the finished ethanol composition may be blended withgasoline for motor vehicles such as automobiles, boats and small pistonengine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited herein and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with one or more otherembodiments, as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol comprising: hydrogenatingacetic acid and/or an ester thereof in a reactor in the presence of acatalyst to form a crude ethanol product comprising ethanol, water,ethyl acetate and acetic acid; esterifying a portion of the crudeethanol product in an esterification reactor to esterify acetic acid andform an esterified stream; separating a portion of the esterified streamin a first distillation column to yield a first distillate comprisingacetaldehyde and ethyl acetate, and a first residue comprising ethanol,acetic acid, ethyl acetate and water; separating a portion of the firstresidue in a second distillation column to yield a second residuecomprising acetic acid and an overhead vapor comprising ethanol, ethylacetate and water; removing water from at least a portion of theoverhead vapor to yield an ethanol mixture stream having a lower watercontent than the at least a portion of the overhead vapor; andseparating at least a portion of the ethanol mixture stream in a thirddistillation column to yield a third distillate comprising ethyl acetateand a third residue comprising ethanol and less than 8 wt. % water. 2.The process of claim 1, further comprising removing one or morenon-condensable gases from the crude ethanol product prior toesterifying.
 3. The process of claim 1, wherein the crude ethanolproduct comprises less than 35 wt. % acetic acid.
 4. The process ofclaim 1, wherein the esterified stream comprises less than 10 wt. %acetic acid.
 5. The process of claim 1, wherein the total conversion ofacetic acid in the reactor and the esterification reactor is greaterthan 90%.
 6. The process of claim 1, wherein the esterification reactorcomprises an acid catalyst.
 7. The process of claim 1, wherein water isremoved from the overhead vapor using a water separator selected fromthe group consisting of an adsorption unit, membrane, extractive columndistillation, molecular sieves, and combinations thereof.
 8. The processof claim 1, wherein the third distillate is fed to the first column. 9.The process of claim 1, wherein the first column is an extractive columnand further comprising introducing an extractive agent to the firstcolumn.
 10. A process for producing ethanol comprising: hydrogenatingacetic acid and/or an ester thereof in a reactor in the presence of acatalyst to form a crude ethanol product comprising ethanol, water,ethyl acetate and acetic acid; separating a portion of the crude ethanolproduct in a first distillation column with a side car reactor foresterifying acetic acid in a sidedraw from the first distillationcolumn, wherein the first distillation column yields a first distillatecomprising acetaldehyde and ethyl acetate, and a first residuecomprising ethanol, acetic acid, ethyl acetate and water; separating aportion of the first residue in a second distillation column to yield asecond residue comprising acetic acid and an overhead vapor comprisingethanol, ethyl acetate and water; removing water from at least a portionof the overhead vapor to yield an ethanol mixture stream having a lowerwater content than the at least a portion of the overhead vapor; andseparating at least a portion of the ethanol mixture stream in a thirddistillation column to yield a third distillate comprising ethyl acetateand a third residue comprising ethanol and less than 8 wt. % water. 11.The process according to claim 10, wherein the sidedraw to the side carreactor is taken from a location below the crude ethanol product fed tothe first distillation column.
 12. The process according to claim 10,wherein the esterification of acetic acid is catalyzed using an acidcatalyst.
 13. The process of claim 10, wherein water is removed from theoverhead vapor using a water separator selected from the groupconsisting of an adsorption unit, membrane, extractive columndistillation, molecular sieves, and combinations thereof.
 14. Theprocess of claim 10, wherein the first column is an extractive columnand further comprising introducing an extractive agent to the firstcolumn.
 15. A process for producing ethanol comprising: hydrogenatingacetic acid and/or an ester thereof in a reactor in the presence of acatalyst to form a crude ethanol product comprising ethanol, water,ethyl acetate and acetic acid; separating a portion of the crude ethanolproduct in a first distillation column with an integrated reboilerreactor for esterifying acetic acid in a reboiler loop of the firstdistillate column, wherein the first distillation column yields a firstdistillate comprising acetaldehyde and ethyl acetate, and a firstresidue comprising ethanol, acetic acid, ethyl acetate and water;separating a portion of the first residue in a second distillationcolumn to yield a second residue comprising acetic acid and an overheadvapor comprising ethanol, ethyl acetate and water; removing water fromat least a portion of the overhead vapor to yield an ethanol mixturestream having a lower water content than the at least a portion of theoverhead vapor; and separating at least a portion of the ethanol mixturestream in a third distillation column to yield a third distillatecomprising ethyl acetate and a third residue comprising ethanol and lessthan 8 wt. % water.
 16. The process of claim 15, wherein the integratedreboiler reactor comprises an acid catalyst.
 17. The process of claim15, wherein the first column is an extractive column and furthercomprising introducing an extractive agent to the first column.
 18. Aprocess for producing ethanol comprising: hydrogenating acetic acidand/or an ester thereof in a reactor in the presence of a catalyst toform a crude ethanol product comprising ethanol, water, ethyl acetateand acetic acid; separating a portion of the crude ethanol product in afirst distillation column to yield a first distillate comprisingacetaldehyde and ethyl acetate, and a first residue comprising ethanol,acetic acid, ethyl acetate and water; esterifying a portion of the firstresidue in an esterification reactor to esterify acetic acid and form anesterified first residue; separating a portion of the esterified firstresidue in a second distillation column to yield a second residuecomprising acetic acid and an overhead vapor comprising ethanol, ethylacetate and water; removing water from at least a portion of theoverhead vapor to yield an ethanol mixture stream having a lower watercontent than the at least a portion of the overhead vapor; andseparating at least a portion of the ethanol mixture stream in a thirddistillation column to yield a third distillate comprising ethyl acetateand a third residue comprising ethanol and less than 8 wt. % water. 19.The process of claim 18, wherein the esterification reactor comprises anacid catalyst.
 20. A process for producing ethanol comprising: providinga crude ethanol product comprising ethanol, water, ethyl acetate andacetic acid; separating a portion of the crude ethanol product in afirst distillation column with a side car reactor for esterifying aceticacid in a sidedraw from the first distillation column, wherein the firstdistillation column yields a first distillate comprising acetaldehydeand ethyl acetate, and a first residue comprising ethanol, acetic acid,ethyl acetate and water; separating a portion of the first residue in asecond distillation column to yield a second residue comprising aceticacid and an overhead vapor comprising ethanol, ethyl acetate and water;removing water from at least a portion of the overhead vapor to yield anethanol mixture stream having a lower water content than the at least aportion of the overhead vapor; and separating at least a portion of theethanol mixture stream in a third distillation column to yield a thirddistillate comprising ethyl acetate and a third residue comprisingethanol and less than 8 wt. % water.